Alkenyl succinic anhydrides have been prepared by the addition reaction of olefins and maleic anhydride. Generally, the olefin is used in molar excess, for example from about 1.5 to about 5.0 moles of olefin per mole of maleic anhydride to obtain an effective addition reaction. The reaction can be conducted by heating the reactants at a temperature in the range of about 120.degree. to about 250.degree. C. or more for a period of time of from about 0.5 hour to about 24 hours or more. Preferably, the reaction is conducted at a temperature of 165.degree. to 225.degree. C. for a period of 2 to 8 hours.
Various processes have been developed to improve the efficiency of the addition reaction of an olefin and maleic anhydride. U.S. Pat. No. 3,202,679 discloses a process under which the olefin/maleic anhydride addition reaction is conducted under conditions to convert maleic acid impurity in the reaction system to fumaric acid. U.S. Pat. No. 3,412,111 discloses a process employing minor amounts of a hydroxy aromatic or an amino aromatic compound to reduce polymer formation during the addition reaction. U.S. Pat. No. 3,819,660 discloses the use of a catalytic amount of p-alkylbenzene sulfonic acid and 1-3 weight parts of acetic anhydride per part of the sulfonic acid to suppress tar formation during the reaction of 168 to 800 M.W. alkene with maleic anhydride. U.S. Pat. No. 4,255,340 discloses a process for preparing alkenyl succinic anhydride by the addition reaction of an olefin and maleic anhydride in the presence of a catalytic amount brominated hydroxy compound. U.S. Pat. No. 4,396,774 discloses a process for the production of alkenyl succinic anhydrides by the addition reaction of olefin and maleic anhydride in the presence of a catalytic amount of an alkyl aluminum halide.
The alkenyl succinic anhydride and derivatives thereof are useful as additives for fuels, lubricating oil compositions, curing agents for epoxy resins, plasticizers, surfactants etc. Alkenyl succinic anhydrides wherein the alkenyl substituent has from about 6 to 18 carbon atoms are of value as a raw material for the production of C.sub.6 -C.sub.18 alkyl diperoxy succinic acid, i.e. C.sub.6 -C.sub.18 alkyl substituted butanediperoxoic acid, an effective bleaching agent. See U.S. Pat. No. 4,482,349 issued Nov. 13, 1984 to James M. Mayer.
It has been found that the prior methods of preparing alkenyl succinic anhydrides suitable as precursors for the preparation of C.sub.6 -C.sub.18 alkyl succinic anhydride by catalytic hydrogenation, is initially a two phase liquid reaction system. The two phase liquid reaction system suffers the disadvantage of prolonged reaction times, excessive use of energy to maintain the reactants in intimate contact to effect reaction and the formation of undesired polymerization by-products. It has been found that these disadvantages can be overcome by the process of conducting the reaction of a C.sub.6 -C.sub.18 alkene with maleic anhydride in the presence of sufficient amount of a C.sub.6 -C.sub.18 alkyl succinic anhydride to maintain the reactants in a single liquid phase.